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Recently in discussing folded dipole antennas, I mentioned that I had not come across the concept of a quarter-wave folded dipole with high-impedance feed until following up a reference to the original American TV-sound antenna erected on the Empire State Building in the late 1930s. Memory is fallible - I now realise that the dual-band W6BCX Multee (Fig 1), described in TT over 30 years ago and reproduced in all editions ofAmateur Radio Techniques (but in which an error has crept in giving the feed impedance of the λ/4 element as 600Ω instead of up to 6000Ω although this does not affect the dimensions or matching) has the top radiator (as used on the higher of the two bands) in the form of a λ/4 folded dipole, fed from 50Ω coaxial cable by means of the vertical section which forms a linear impedance transformer on the higher band while acting as a top-loaded vertical radiator on the lower band.

Fig 1
Fig 1: The Multee two-band antenna using L1 as a λ/4 0 folded dipole on the higher band, with the high feed-impedance (up to 6000Ω) provided by L2 acting as a linear transformer (λ/2 times velocity factor).

This antenna, described in various editions of The Radio Handbook, is claimed to form a compact antenna which can be used 'with excellent results on 1.8/3.5MHz (with 52ft vertical section and 70ft span) and 3.5/7MHz (with 28ft vertical section and 35ft span). The `feedline' should be held as vertical as possible, since it radiates vertically polarized signals on the lower (fundamental) frequency. A good 'earth' system, preferably of buried or elevated radials, is desirable for the lower-frequency band but of little importance on the higher band with horizontally-polarized radiation from the λ/4 'top'.